The present invention relates generally to short wavelength optical systems and elements for use therein, optical projection lithography methods and photolithography, and particularly to optical photolithography fluoride crystal elements for use in optical photolithography systems and short wavelength optical systems utilizing ultraviolet light (UV) wavelengths below 194 nm, such as UV lithography systems utilizing wavelengths in the 193 nm region and the 157 nm region.
Projection optical photolithography methods/systems that utilize the ultraviolet wavelengths of light below 194 nm provide benefits in terms of achieving smaller feature dimensions. Such methods/systems that utilize ultraviolet wavelengths in the 157 nm and the 193 nm wavelength regions have the potential of improving the manufacturing of integrated circuits with smaller feature sizes but the commercial use and adoption of below 194 nm UV in high volume mass production of integrated circuits has been slow. Part of the slow progression to below 194 nm UV by the semiconductor industry has been due to the lack of economically manufacturable fluoride cubic crystal optical elements with high performance at such short wavelengths. For the benefit of ultraviolet photolithography in the 157 nm region such as the emission spectrum window of a fluorine excimer laser and the 193 nm region such as the ArF excimer laser emission spectrum to be utilized in the manufacturing of integrated circuits there is a need for fluoride crystal optical elements that have beneficial optical properties and that can be designed for and utilized with below 194 nm UV photons. The Argon Fluoride emits at xcx9c193 nm and the Fluorine (F2) excimer emits at xcx9c157 nm, and for various optical applications it is preferable to have such short wavelengths of light less than 194 nm. For use with optical systems with Fluorine (F2) lasers or Argon Fluoride lasers, the preferred crystal material for optical elements has been calcium fluoride, a cubic fluoride crystal.
The invention includes a method of making a  less than 194 nm wavelength transmitting calcium fluoride crystal optical lithography element for transmitting wavelengths less than about 194 nm along an optical axis with minimal intrinsic birefringence. The method includes providing an optical element calcium fluoride crystal with an input face {100} crystal plane and forming said input face {100} crystal plane into an optical lithography element surface of an optical lithography element having an optical axis, with the optical axis aligned with a  less than 100 greater than  crystal direction of the calcium fluoride crystal.
The invention includes a  less than 194 nm wavelength transmitting calcium fluoride crystal optical lithography element for transmitting wavelengths less than 194 nm with minimal intrinsic birefringence. The optical lithography element is comprised of an optical calcium fluoride crystal with a {100} crystal plane and a  less than 100 greater than  crystal direction with the optical element having an optical axis aligned with the  less than 100 greater than  calcium fluoride crystal direction.
The invention includes a method of making a fluoride crystal optical element for transmitting short wavelengths of light ( less than 194 nm) along an optical axis with minimal intrinsic birefringence. The method includes providing an optical element optical fluoride crystal with an input face {100} crystal plane and forming the input face {100} crystal plane into an optical element surface of an optical element having an optical axis with the optical axis aligned with a  less than 100 greater than  crystal direction of the optical fluoride crystal.
The invention includes an optical element for transmitting wavelengths less than about 194 nm with minimal intrinsic birefringence. The optical element is comprised of a cubic optical fluoride crystal with a {100} crystal plane and a  less than 100 greater than  crystal direction with the optical element having an optical axis aligned with the  less than 100 greater than  crystal direction.
The invention includes a below 194 nm wavelength transmitting lens with minimal intrinsic birefringence comprised of a cubic optical fluoride crystal with a {100} crystal plane and a  less than 100 greater than  crystal direction. The lens has a curved optical surface and an optical axis aligned with the  less than 100 greater than  crystal direction and normal to the {100} crystal plane.
The invention includes a below 194 nm wavelength transmitting beam splitter cube with minimal intrinsic birefringence. The beam splitter cube is comprised of a cubic optical fluoride crystal with a {100} crystal plane and a  less than 100 greater than  crystal direction with the beam splitter cube face parallel to the {100} crystal plane and an optical axis aligned with the  less than 100 greater than  crystal direction.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the invention as described in the written description and claims hereof, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework to understanding the nature and character of the invention as it is claimed.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s) of the invention, and together with the description serve to explain the principles and operation of the invention.